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The dynamics of cylindrical bodies in a rotating horizontal cylinder filled with a high-viscosity fluid is experimentally studied. The cylinder rotation rate is modulated. When the cylinder rotates uniformly, the bodies are located near the cylindrical wall and rotate together with the cylinder. The dynamics of bodies depending on the amplitude and frequency of modulation of the cylinder rotation rate is studied in detail. It is found that the cylindrical bodies undergo azimuthal and rotational oscillations. When the critical amplitude of modulation is reached, the bodies repel from the wall and obtain a steady state position at some distance from the wall.

In 1971, Zel’dovich predicted that quantum fluctuations and classical waves reflected from a rotating absorbing cylinder will gain energy and be amplified. This concept, which is a key step towards the understanding that black holes may amplify quantum fluctuations, has not been verified experimentally owing to the challenging experimental requirement that the cylinder rotation rate must be larger than the incoming wave frequency. Here, we demonstrate experimentally that these conditions can be satisfied with acoustic waves. We show that low-frequency acoustic modes with orbital angular momentum are transmitted through an absorbing rotating disk and amplified by up to 30% or more when the disk rotation rate satisfies the Zel’dovich condition. These experiments address an outstanding problem in fundamental physics and have implications for future research into the extraction of energy from rotating systems. Acoustic waves that carry orbital angular momentum are amplified as they pass through an absorbing disk when the rotation rate exceeds the frequency of the incident wave, thus providing an experimental demonstration of Zel’dovich amplification.

We use direct numerical simulations to study convection in rotating Rayleigh-B & eacute;nard convection in horizontally confined geometries of a given aspect ratio, with the walls held at fixed temperatures. We show that this arrangement is unconditionally unstable to flow that takes the form of wall-adjacent convection rolls. For wall temperatures close to the temperatures of the upper or lower boundaries, we show that the base state undergoes a Hopf bifurcation to a state comprised of spatiotemporal oscillations - 'wall modes' - precessing in a retrograde direction. We study the saturated nonlinear state of these modes, and show that the velocity boundary conditions at the upper and lower boundaries are crucial to the formation and propagation of the wall modes: asymmetric velocity boundary conditions at the upper and lower boundaries can lead to prograde wall modes, while stress-free boundary conditions at both walls can lead to wall modes that have no preferred direction of propagation.

Three-dimensional non-rotating odd viscous liquids give rise to Taylor columns and support axisymmetric inertial-like waves (J. Fluid Mech., vol. 973, 2023, A30). When an odd viscous liquid is subjected to rigid-body rotation however, there arise in addition a plethora of other phenomena that need to be clarified. In this paper, we show that three-dimensional incompressible or two-dimensional compressible odd viscous liquids, rotating rigidly with angular velocity $\\varOmega$, give rise to both oscillatory and evanescent inertial-like waves or a combination thereof (which we call of mixed type) that can be non-axisymmetric. By evanescent, we mean that along the radial direction, typically when moving away from a solid boundary, the velocity field decreases exponentially. These waves precess in a prograde or retrograde manner with respect to the rotating frame. The oscillatory and evanescent waves resemble respectively the body and wall-modes observed in (non-odd) rotating Rayleigh–Bénard convection (J. Fluid Mech., vol. 248, 1993, pp. 583–604). We show that the three types of waves (wall, body or mixed) can be classified with respect to pairs of planar wavenumbers $\\kappa$ which are complex, real or a combination, respectively. Experimentally, by observing the precession rate of the patterns, it would be possible to determine the largely unknown values of the odd viscosity coefficients. This formulation recovers as special cases recent studies of equatorial or topological waves in two-dimensional odd viscous liquids which provided examples of the bulk–interface correspondence at frequencies $\\omega <2\\varOmega$. We finally point out that the two- and three-dimensional problems are formally equivalent. Their difference then lies in the way data propagate along characteristic rays in three dimensions, which we demonstrate by classifying the resulting Poincaré–Cartan equations.

We compute the flow induced by the steady translation of a rigid sphere along the axis of a large cylindrical container filled with a low-viscosity fluid set in rigid-body rotation, the sphere being constrained to spin at the same rate as the undisturbed fluid. The parameter range covered by the simulations is similar to that explored experimentally by Maxworthy (J. Fluid Mech., vol. 40, 1970, pp. 453–479). We describe the salient features of the flow, especially the internal characteristics of the Taylor columns that form ahead of and behind the body and the inertial wave pattern, and determine the drag and torque acting on the sphere. Torque variations are found to obey two markedly different laws under rapid- and slow-rotation conditions. The corresponding scaling laws are predicted by examining the dominant balances governing the axial vorticity distribution in the body vicinity. Results for the drag agree well with the semi-empirical law proposed for inertialess regimes by Tanzosh & Stone (J. Fluid Mech., vol. 275, 1994, pp. 225–256). This law is found to apply even in regimes where inertial effects are large, provided that rotation effects are also large enough. Influence of axial confinement is shown to increase dramatically the drag in rapidly rotating configurations, and the container length has to be approximately a thousand times larger than the sphere for this influence to become negligibly small. The reported simulations establish that this confinement effect is at the origin of the long-standing discrepancy existing between Maxworthy's results and theoretical predictions.

The orientation dynamics of inertialess prolate and oblate spheroidal particles in a directly simulated spanwise-rotating turbulent channel flow has been investigated by means of an Eulerian–Lagrangian point-particle approach. The channel rotation and the particle shape were parameterized using a rotation number Ro and the aspect ratio λ, respectively. Eleven particle shapes 0.05 ≤ λ ≤ 20 and four rotation rates 0 ≤ Ro ≤ 10 have been examined. The spheroidal particles retained their almost isotropic orientation in the core region of the channel, despite the significant mean shear rate set up by the Coriolis force. Irrespective of channel rotation rate Ro, rod-like spheroids tend to align in the streamwise direction, while disk-like particles are oriented in the wall-normal direction. These trends were accentuated with increasing departure from sphericity λ = 1. The changeover from the isotropic orientation mode in the centre to the highly anisotropic near-wall orientation mode commenced further away from the suction-side wall with increasing Ro, whereas the particle orientations on the pressure side of the rotating channel remained essentially unaffected by Ro. We observed that the alignments of the fluid rotation vector with the Lagrangian stretching direction were similarly unaffected by the imposed system rotation, except that the de-alignment set in deeper into the core at high Ro. This contrasts with the well-known substantial impact of system rotation on the velocity and vorticity fields. Similarly, slender rods and flatter disks were aligned with the Lagrangian stretching and compression directions, respectively, for all Ro considered, except in the vicinity of the walls. The typical near-wall de-alignment extended considerably further away from the suction-side wall at high Ro. We conjecture that this phenomenon reflects a change in the relative importance of mean shear and small-scale turbulence caused by the Coriolis force. Preferential particle alignment with Lagrangian stretching and compression directions are known from isotropic and anisotropic turbulence in inertial reference systems. The present results demonstrate the validity of this principle also in a non-inertial system.

The flow with low shear inside a bladeless mixer is characterized experimentally. This soft mixer, inspired by the precession of the Earth, consists of a cylindrical container rotating around its axis and tilted from the vertical. For low Froude numbers, the free surface remains horizontal, thus generating a forcing on the tilted rotating fluid. As in the case of a precessing cylinder, this forcing excites global inertial modes (Kelvin modes) which become resonant when the height of fluid is equal to a multiple of a half-wavelength. Ekman pumping saturates the amplitude of the mode at a value proportional to the square root of the Reynolds number. For sufficiently large tilt angles and Reynolds numbers, the global mode destabilizes via a parametric triadic instability involving two additional Kelvin modes. The viscous threshold of the instability can be predicted analytically with no fitting parameter and is in excellent agreement with the experimental results. This instability generates a strong mixing which is as efficient as the one achieved using a classical Rushton turbine, but with a shear 20 times smaller. This simple bladeless mixer is thus an excellent candidate for large scale bioreactors where mixing is needed to enhance gas exchanges but where shear is harmful for fragile cells. Preliminary results obtained for the growth of microalgae (dinoflagellates) in such photobioreactors suggest that it could be a technological breakthrough in biotechnologies.

Rotating machines is an essential part of any manufacturing industry. The sudden breakdown of such machines due to improper maintenance can also lead to the industries' shutdown. The era of the 4th industrial revolution is taking its major shape concerning maintenance strategies, notable being in predictive maintenance. Fault prediction and diagnosis is the major concern in predictive maintenance as this is the major issue faced by all the maintenance engineers. Most of the bibliometric literature review studies that are accessible focus on fault diagnosis in rotating machines, mainly focusing on a single type of fault. However, there isn't a thorough analysis of the literature that focuses on the \"multi-fault diagnosis using multi-sensor data\" aspect of rotating machines. In this regard, this paper reviews the literature on the “multi-Fault diagnosis using multi-sensor data fusion” of Industrial Rotating Machines employing Machine learning/Deep learning techniques. A hybrid bibliometric approach was used to analyze articles from the “Web of Science” and “Scopus” Database for the last 10 years. The method for literature analysis used, is quantitative as well as qualitative, as not only the traditional approach (bibliometric and network analysis) but also a novel method named ProKnow-C is used, and it entails a number of phases, that includes intelligent and extensive filtering from the large set of results and finally selecting the articles that are more pertinent to the research theme. Based on available publications, an analysis is performed on year-by-year publication data, article types, linguistic distribution of articles, funding sponsors, affiliations, citation analysis and the relationship between keywords, authors, etc. to provide an in-depth vision of research trends in the related area. The paper also focuses on the maintenance strategies, predictive maintenance approaches, AI algorithms, Multi sensor data fusion, challenges, and future directions in “multi-fault diagnosis using multi-sensor data fusion” in rotating machines. The foundational work done in the field, the most prolific papers and the key research themes within the research area are all identified in this bibliometric survey.

Many rotating machines utilize a fluid-type bearing. Despite their reliability and high load capacity, these bearings often show instabilities due to the interaction between the fluid media and the rotating shaft. These instabilities, known as oil-whirl and oil-whip, occur due to a Hopf bifurcation; being the parameter the shaft speed. Identifying the type of bifurcation, either sub-critical or super-critical, is an important task to determine the safety of the machines near the instability speed, and it tells whether one experiences oil-whip or oil-whirl. This work presents an approach, based on the center manifold reduction (CMR) method, to obtain limit cycles near Hopf bifurcations of rotors supported on fluid-film bearings. The basis of the method is the obtention of the center manifold of the system, which allows one to assess the type of bifurcation at hand. To obtain the center manifold, the parameterization method for invariant manifolds is used, which is a powerful tool to obtain invariant manifolds of high-dimensional dynamical systems. The proposed method is evaluated by comparing its results with an open-source numerical continuation package (MATCONT) in two systems: a simple and a realistic rotor system. The results show that the CMR, together with the parameterization method, can be used reliably to learn if the rotor system presents sub- or super-critical bifurcations, to perform parametric studies with different bearing properties, and also to predict the amplitude of the limit cycles.

Rayleigh–Bénard convection in rotating spherical shells can be considered as a simplified analogue of many astrophysical and geophysical fluid flows. Here, we use three-dimensional direct numerical simulations to study this physical process. We construct a dataset of more than 200 numerical models that cover a broad parameter range with Ekman numbers spanning $3\\times 10^{-7}\\leqslant E\\leqslant 10^{-1}$ , Rayleigh numbers within the range $10^{3}

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